The power output of an array of solar units, i.e. an array of photovoltaic (PV) panels or an array of panels for solar thermal power production, drops when the sun is covered during inclement weather or during a cloudy day. A dispatcher of a utility generally starts standby power systems to supplement or replace the power output of a solar array during periods of low or nonexistent solar influx.
The variability in power output of a solar unit array during periods of cloud coverage due to a drop in power output negatively influences the stability of the electric grid to which the utility supplies electricity, particularly when the power output of the utility constitutes a significant portion of the generating capacity of the electric grid. The ability of supplying a substantially constant level of electricity to a grid is becoming increasingly more important due to the growing emphasis placed on alternative energy sources by various governmental agencies. California utilities, for example, are obliged by state law to buy 33 percent of their power from renewable sources such as solar panels by 2020. Accordingly, utilities would have to be able to immediately supplement the power when the power output suddenly drops during periods of cloud coverage.
In a typical solar thermal based power plant, an array of parabolic mirrors concentrate solar energy onto receivers containing a heat transfer fluid. The solar energy is optimized by means of a central computerized tracking facility. The heat transfer fluid is circulated and heated through the receivers, and the heat is released to a series of heat exchangers to generate superheated steam. The superheated steam powers a turbogenerator to produce electricity delivered to an electric grid. An oil heater is employed to generate sufficiently hot heat transfer fluid which will produce superheated steam beyond daylight hours. Such backup or standby power systems suffer from a relatively slow starting time of approximately 30 minutes, and the power level of the grid will invariably drop during the interim period until the backup or standby power system becomes operational.
Another prior art solution to eliminate the hourly variations of power output is the use of batteries of a high storage capacity. No adjustment is required as a controller automatically limits the power produced by the batteries in response to the power produced by the solar array. However, the cost of these large batteries of a high storage capacity is prohibitive.
The present invention provides a method and system for standby power generation supplementing solar arrays during periods of cloud coverage without a significant power drop.
In addition, the present invention provides a method and system for standby power generation supplementing solar arrays during periods of cloud coverage that has a quicker startup time than that of a prior art system.
Furthermore, the present invention provides a method and system for standby power generation supplementing solar arrays during periods of cloud coverage that is cost effective.
Other advantages of the invention will become apparent as the description proceeds.